Resin molding, method for manufacturing the same, and metal mold for manufacturing the same

ABSTRACT

A resin molding is provided. A main body is comprised of 100 parts by weight of thermoplastic resin and 0.1 to 4 parts by weight of bright material having the aspect ratio of 30 to 50. A main body has a design surface formed with a groove. The lower limit of the depth of the groove is set to 0.3 mm and the upper limit of the depth of the groove is set to 0.5 mm.

This application claims priority from Japanese Patent Application No.2008-070801 filed Mar. 19, 2008, the entire contents of which are hereinincorporated by reference.

BACKGROUND

The present invention relates to a resin molding, a method formanufacturing the resin molding and a metal mold for manufacturing theresin molding by injection molding method, and more particularly, to ametallic tone resin molding that prevents generation of appearancedefects and has a color with metallic feeling caused by bright materialto have excellent design properties, and a method and a metal mold formanufacturing the metallic tone resin molding.

A four-wheel vehicle provided with a manual transmission (MT) includes ashift lever that is used to select the combination of gears of the MT bya driver. The shift lever is mounted on a floor in a vehicle cabin, aninstrument panel (dashboard), a column for supporting a steering wheel,or the like. The shift lever includes a shift knob that is grasped by adriver. The shift knob includes a garnish, such as a shift garnish or ashift knob garnish. The shift garnish has letters or straight linescomprised of a plurality of grooves, that indicate the gear position ofthe MT. The shift garnish may have a color with metallic tone brightfeeling.

An MT shift garnish of the four-wheel vehicle is one of significantfactors for determining the impression of a driver's seat, and is anappreciative object under both sunlight and indoor light. Accordingly, apainted-component having a silver metallic color with the brightfeeling, has been widely used as the MT shift garnish to obtain highdesign properties. However, volatile organic compound (VOC) generateddue to the painting causes an environmental load, and thus the dischargeof the VOC has been regulated in recent years (for example, AirPollution Control Act of Japan (amended in 2004)). For this reason,there is a demand for a shift garnish that is formed without painting.

An injection molding method using resin material which colored with acolorant such as pigment or dye is known as such a paintless method. Tocolor the resin material with a silver metallic color having high brightfeeling, bright material such as aluminum powder or mica powder is addedto the resin material. Particularly, to obtain high metallic feeling orpearl feeling, it is necessary to add the bright material.

However, appearance defects such as a “weld line” or a “flow mark” arelikely to occur when using such resin material to which the brightmaterial is added. In molding, a collision or a turbulent flow of theresin material occurs in the metal mold and thus flowability of theresin material deteriorates. Accordingly, the bright material is likelyto be orientated in the metal mold. This orientation results in the weldline or the flow mark. In particular, the appearance defects such as theweld line or the flow mark are likely to occur when rectangular groovesare formed on a design surface of an MT shift garnish. As shown in FIG.10A, the design surface of the MT shift garnish is formed with therectangular grooves which indicate operative positions and directions ofa shift lever. Therefore, unlike the painting, it is very hard tomaintain high design properties in the resin molding. That is, it isvery hard to secure the silver metallic tone which has high qualityfeeling while preventing the generation of the appearance defects.Further, the appearance defects such as the weld line or the flow markare also likely to occur when the resin material contains brightmaterial having high aspect ratio since the flowability of the resinmaterial is decreased due to the bright material.

Patent Document 1 discloses a method for mixing 0.1 to 20.0 parts byweight of a bright material which has a maximum outer diameter in therange of 10 [μm] to 1 [mm] to 100 parts by weight of a thermoplasticresin so that a mean particle spacing D of the bright material and aweld width H satisfy an expression D≧H. This method disclosed in PatentDocument 1 can suppress the weld line, but cannot completely eliminatethe weld line. Further, this method cannot be applied to bright materialthat has a maximum outer diameter smaller than 10 [μm].

Patent Document 2 discloses a method for eliminating the weld line byadding a titanium oxide, a lead oxide, or a zinc oxide, which is calleda weld-eliminating agent, to a resin. However, this method disclosed inPatent Document 2 increases cost and causes difficulty in colormatching. Although Patent Document 2 mentions a high quality color tonesuch as a metallic tone or a pearl tone, can be obtained by thedisclosed method, the metallic feeling significantly deteriorates whenthe weld-eliminating agent is added in actuality.

Patent Document 3 discloses a method for adding 0.05 to 10 parts byweight of metal powder that has the aspect ratio in the range of 3 to 15and the mean particle diameter in the range of 10 to 300 [μm], andadding predetermined parts by weight of a thermoplastic resin (forexample, polyethylene or polypropylene) that has a reactive group otherthan a polyamide resin, which suppresses a weld line, in order to obtaina metallic tone polyamide resin molding which has no weld line andexcellent appearance without painting the resin molding. However, PatentDocument 3 is completely silent about a molding formed with rectangulargrooves on a design surface thereof. Further, Patent Document 3 does notdiscuss the degree of the metallic feeling.

Patent Document 1: Japanese Patent Publication No. 04-027932A

Patent Document 2: Japanese Patent Publication No. 08-239505A

Patent Document 3: Japanese Patent Publication No. 2000-086889A

Therefore, in the above related-art, it is difficult to obtain highdesign properties in a molding such as a garnish of an automotive partwhich has a complex shape in a design surface thereof by securing themetallic tone like the painted-component while preventing the generationof the appearance defects.

That is, in the related-art, the painting must be performed on the resinmolding in order to obtain the high design properties. Withoutperforming the painting, the bright feeling cannot added to the resinmaterial to prevent the generation of the appearance defects.Accordingly, a color of the molding is limited to a black or the like.In this case, the design properties of the molding are deteriorated.

SUMMARY

It is therefore an object of the invention is to provide a metallic toneresin molding that secures high design properties obtained by a metallicfeeling and prevents generation of appearance defects, even though aplurality of rectangular grooves are formed on a design surface of theresin molding, and a method and a metal mold for manufacturing themetallic tone resin molding.

According to an aspect of an exemplary embodiment of the presentinvention, there is provided a resin molding, comprising: a main bodywhich is comprised of 100 parts by weight of thermoplastic resin and 0.1to 4 parts by weight of bright material having the aspect ratio of 30 to50, wherein a main body has a design surface formed with a groove; andwherein the lower limit of the depth of the groove is set to 0.3 mm andthe upper limit of the depth of the groove is set to 0.5 mm.

With this configuration, since the aspect ratio Y of the bright materialis relatively high, that is, in the range of 30 to 50, it is possible toobtain high metallic feeling due to the bright material. Further, sincethe depth of the groove is limited absolutely, it is possible to preventthe generation of appearance defects, such as a weld line or a flowmark. For this reason, it is not necessary to perform painting on acomponent which requires high design properties, such as variousgarnishes of automotive parts.

According to another aspect, there is also provided a method formanufacturing a resin molding, comprising: laminating a plurality ofplates to form a cavity and a gate through which resin material isinjected into the cavity; injecting the resin material which iscomprised of 100 parts by weight of thermoplastic resin and 0.1 to 4parts by weight of bright material, into the cavity through the gate;hardening the resin material to form the resin molding; and separatingthe plates to extract the resin molding from the cavity, wherein theplates are formed such that the resin molding includes a main bodyhaving a round-shaped design surface formed with a plurality ofrectangular-shaped grooves, the longest groove of which extends in afirst direction; and wherein the plates are formed such that the gateextends toward a center of the round-shaped design surface and at anangle range of 45°±30° with respect to the first direction.

With the above method, the resin flows through the gate which isextended at the angle range of 45°±30° with respect to the firstdirection (an extending direction of the longest groove of therectangular-shaped grooves). Supplying the resin material which containsthe bright material at this gate angle (range), it is possible to reducethe degree of the appearance defects such as a weld line or a flow markas compared with the other gate angle (range).

According to still another aspect, there is provided a metal mold formanufacturing a resin molding, comprising: a first plate formed with asprue; and a second plate; wherein the first plate and the second plateare formed such that a cavity, a gate and a runner are formed when thefirst plate is laminated on the second plate so that resin material isinjected from the sprue into the cavity through the runner and the gateto form the resin molding; wherein the first plate and the second plateare formed such that the resin molding includes a main body having around-shaped design surface formed with a plurality ofrectangular-shaped grooves, the longest groove of which extends in afirst direction; and wherein the first plate and the second plate areformed such that the gate extends toward a center of the round-shapeddesign surface and at an angle range of 45°±30° with respect to thefirst direction.

With the above configuration, the gate is provided so as to extend atthe angle range of 45°±30° with respect to the first direction (anextending direction of the longest groove of the rectangular-shapedgrooves). Supplying the resin material which contains the brightmaterial at this gate angle (range), it is possible to reduce the degreeof the appearance defects such as a weld line or a flow mark as comparedwith the other gate angle (range).

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects of the present invention will become moreapparent by describing in detail exemplary embodiments thereof withreference to the accompanying drawings, wherein:

FIG. 1 is a explanatory diagram illustrating relationship between arange of the depth of groove formed on a design surface and a range ofthe aspect ratio of a bright material according to Embodiments 1 to 3 ofthe present invention;

FIG. 2 is a explanatory diagram illustrating an example of definition ofthe aspect ratio according to Embodiments 1 to 3;

FIG. 3 is a perspective cross-sectional view illustrating an example ofa groove of a resin molding according to Embodiments 1 to 3;

FIG. 4 is a cross-sectional view illustrating another example of thegroove according to Embodiments 1 to 3;

FIG. 5 is a view illustrating a relationship between the depth of thegroove and appearance defects according to Embodiments 1 to 3;

FIG. 6 is a view illustrating an example of a test piece according toEmbodiment 1 to 3;

FIG. 7 is a view illustrating an example in which resin flows in adirection parallel to a long side of the groove according to Embodiment1;

FIG. 8 is a view illustrating an example in which the resin flows in adirection parallel to a short side of the groove according to Embodiment1;

FIG. 9 is a view illustrating an example of a relationship between thegroove on the design surface and a gate angle according to Embodiment 1;

FIG. 10A is a plan view illustrating an example of a design surface ofan MT shift garnish according to Embodiment 1 to 3;

FIG. 10B is a cross-sectional view taken along the line A-A in FIG. 10A;

FIG. 11 is a view illustrating grooves on the design surface of the MTshift garnish according to Embodiment 1;

FIG. 12 is a view illustrating an example of a relationship between ametal mold of the MT shift garnish and a gate angle according toEmbodiments 1 to 3;

FIG. 13 is a view illustrating an example of a plate according toEmbodiments 2 and 3;

FIG. 14 is a flowchart illustrating an example of a manufacturing methodaccording to Embodiment 2;

FIG. 15 is a view illustrating an example of a metal mold capable offorming two moldings at the same time, according to Embodiment 3;

FIG. 16 is a cross-sectional view taken along the line A-A in FIG. 15;and

FIG. 17 is a view illustrating an example of the metal mold capable offorming four moldings at the same time, according to Embodiment 3.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, three preferred embodiments of the present invention willbe described below with reference to the drawings. Embodiment 1corresponds to a metallic tone resin molding 11, Embodiment 2corresponds to a method for manufacturing the metallic tone resinmolding 11 shown in FIG. 15, and Embodiment 3 corresponds to a metalmold that is used for manufacturing the metallic tone resin molding 11and is shown in FIG. 16.

In the embodiments, in order to obtain very high metallic feeling,experiments were performed under a condition where a weld line 30 and aflow mark 32 are likely to be generated on a bright material 10 havinghigh aspect ratio Y that has not been used in the past (FIG. 6 andTables 1 and 2). In addition, a molding material of a resin molding 11,which included a rectangular groove 14 on a design surface 12 thereof,was devised, and the generation states of the weld line 30 and the flowmark 32 were evaluated (FIG. 10A and Tables 3 and 4). As a result, ifthe following factors satisfy respective ranges, it is possible toobtain high design properties.

<Metallic Tone Resin: Condition 1>

In this embodiment, an aspect ratio Y of the bright material 10 is setin the range of 30 to 50 in order to obtain high metallic feeling. It ispreferable that an aspect ratio Y be set in the range of 40 to 50 inorder to obtain very high metallic feeling.

If an aspect ratio Y is high, appearance defects caused by theflowability of a resin, such as the weld line 30 and the flow mark 32,are likely to be generated. In this embodiment, the depth Xd of therectangular groove on the design surface 12 of the molding is set in therange of 0.3 to 0.5 [mm] that corresponds to the lower limit of thevisibility of the design formed by the groove 14. It is preferable thatthe length of the rectangular groove 14 in a direction of a long side 18be set in the range of 0.3 to 0.4 [mm].

0.1 to 4.0 parts by weight of the bright material 10 are added to 100parts by weight of a thermoplastic resin. This range does not affectstrength (impact strength) of the resin molding (Table 1 to be describedbelow). It is preferable that 2.0 to 4.0 parts by weight of the brightmaterial 10 is added to 100 parts by weight of the resin when an opaquethermoplastic resin (for example, AES resin) is used as a base resin toobtain efficient metallic feeling. On the other hand, the metallicfeeling can be secured when 0.1 to 0.5 parts by weight of the brightmaterial 10 is added to transparent resin (PMMA resin or PC resin).Further, to obtain very high metallic feeling, it is preferable that 1.5to 4.0 parts by weight of the bright material 10 is added. 2.0 parts byweight of the bright material is added in Tables 3 and 4 to be describedbelow.

An aspect ratio Y further contributes to metallic feeling as compared toa mean particle diameter, but a mean particle diameter was set in therange of 5 to 40 [μm] in this embodiment. If an aspect ratio Y is higheven though a mean particle diameter is set to 5 [μm], it is possible toobtain very high metallic feeling. Meanwhile, if an aspect ratio Y isset to 10 even though a mean particle diameter is 40 [μm], metallicfeeling does not appear and plastic feeling is significantly strong.

As described above, in the metallic tone resin molding 11 according tothis embodiment, 0.1 to 4 parts by weight of the bright material 10having an aspect ratio Y of 30 to 50 based on 100 parts by weight of athermoplastic resin were added, and the lower limit of the depth Xd ofthe rectangular groove on the design surface 12 was set to 0.3 [mm](Condition 1).

Referring to FIG. 1, in Condition 1, a relationship between an aspectratio Y represented on a vertical axis and a groove depth Xd representedon a horizontal axis corresponds to a range of points ABCD of FIG. 1.

A metallic tone is a property of a material that causes metallicfeeling, and is a property that stimulates a human visual sense by thereflection of natural light or artificial light, which is radiated ontothe design surface 12, on a surface and a body. A metallic tone cannotbe particularly defined by light source colors (for example, RGB), andcannot be specified by reflected colors (Munsell or CMYK). A metallictone depends on at least the degree of reflection on a predeterminedarea and the randomness thereof. For this reason, the presence anddegree of a metallic tone are not physically measured and are measuredby a human visual sense.

In the case of painting, it is possible to significantly increasemetallic feeling with respect to the change of the state of a shadowdepending on the brightness of reflected light and a light sourceposition and reflected colors specified by a Munsell color system or aCMYK color system. Meanwhile, in the case of a resin molding, it ispossible to obtain a predetermined reflected color by adding a colormaterial, but it is difficult to further improve the metallic feeling asdescribed above.

Metal powder such as aluminum powder, a material such as a mineral ormica powder (mica) that may be used in painting, or metallizedpulverized glass may be used as the bright material 10. Aluminum powderis used in embodiments. In the invention, the bright material 10 doesnot have the shape of a sphere and a regular polyhedron and has anaspect ratio Y(=a/b) shown in FIG. 2.

A general-purpose resin or general-purpose engineering plastic may beused as the thermoplastic resin. Examples of the general-purpose resininclude a PMMA resin (methacrylate resin), an ABS resin (containsacrylonitrile, butadiene, and styrene as chief ingredients), and an AESresin (in which ethylene rubber is used instead of butadiene) among ABSresins. Examples of the general-purpose engineering plastic include a PCresin (polycarbonate resin) and a PA resin (polyamide resin). Thethermoplastic resin includes these resins and materials that are addedfor the purpose of target properties or coloring. Meanwhile, aweld-eliminating agent is not used in this embodiment.

FIG. 3 is a cross-sectional and perspective view of a part of the resinmolding 11. The resin molding 11 includes the rectangular groove 14,which is formed by short sides 16 and long sides 18, on the designsurface 12.

The design surface 12 forms the appearance of the resin molding, and isa flat or curved surface. The shape of the design surface 12 correspondsto the shape of a cavity 52 of a metal mold that is used for injectionmolding. A rectangular shape on the design surface 12 is a rectangularshape on a flat or curved surface that is the design surface 12.

The rectangular groove 14 is a concave portion on the design surface 12of the resin molding, and the shape on a flat or curved surface to whichthe concave portion and the design surface 12 are adjacent includes arectangular shape. Even though each of end portions of the rectangularshape has a curvature, the overall shape is a rectangular shape.Accordingly, the rectangular groove 14 is formed.

The groove depth Xd is a distance from the design surface 12 to thebottom of the concave portion in a direction that is oriented toward theinside of the resin molding along a normal line of the design surface12. The groove depth Xd is set in the range of 0.3 to 0.5 [mm]. Thecross-sectional shape of the groove 14 may be a rectangular shape shownin FIG. 3 or a part of a trapezoidal or oval shape shown in FIG. 4.

Operational Advantage of Condition 1

Referring to FIG. 5, if the groove depth Xd of the groove 14 is large,the bright material 10 is likely to be oriented in a region, which isdenoted by reference numeral 24 of FIG. 5, in consideration of arelationship between the flow 20 of a resin including the brightmaterial 10 and the cross-sectional shape of the groove 14, theorientation of the bright material 10 is determined, so that the stateof the orientation is not good and appearance defects are likely to begenerated. Further, the flow mark 32 is likely to be generated in theregion 24. This property becomes remarkable as the length of the longside 18 of the groove 14 is increased. Furthermore, if appearancedefects are generated at a portion near the groove 14, it is notpossible to secure high design properties. Accordingly, designproperties are obtained only by painting after all.

However, as described above, in Condition 1, the condition of the groovedepth Xd is made while the aspect ratio Y of the bright material 10 ishigh, that is, in the range of 30 to 50. Accordingly, the high metallicfeeling caused by the bright material 10 is shown, so that it ispossible to prevent appearance defects that are caused by theorientation near the groove 14. Therefore, the painting may not need tobe performed on parts such as various garnishes of automotive parts thatrequire high design properties.

<Metallic Tone Resin: Condition 2>

Conditions 2 and 3 are conditions obtained by specifying Condition 1with respect to a relationship between the aspect ratio Y and the groovedepth Xd.

When an aspect ratio is denoted by Y and the depth of a rectangulargroove on the design surface 12 is denoted by Xd [mm], the aspect ratioY and the groove depth Xd [mm] are in the ranges satisfying thefollowing Expression 1 or 2 in Condition 2 of this embodiment.

Y≧30, Xd≧0.3, Y≦−100Xd+80   (Expression 1)

Referring to FIG. 1 again, a range, which corresponds to an aspect ratioY of the bright material 10 and a groove depth Xd of the design surface12 of Condition 2, is a triangular range that is formed by connectingpoints ACD of FIG. 1. In Condition 2, a range is formed by partitioningthe range of Condition 1 by a linear expression of Xd, for example, isformed by eliminating a triangular range that has points ABC as apexesand corresponds to the combination of an aspect ratio Y of 50 and agroove depth of 0.5 [mm]. In Condition 2, even though a molding iscomplex so as to include a rectangular groove 14 and grooves (referredto as other grooves 15, see FIG. 10A) for another design shorter than along side 18 of the groove 14, it is possible to secure high metallicfeeling and to prevent appearance defects that are caused by theflowability of a resin.

Y is 30 if Xd is 0.5, and Y is 50 if Xd is 0.3. Accordingly, Expression(1) is obtained by setting up simultaneous equations of Y=aXd+b andsolving the simultaneous equations with respect to a and b. If aplurality of grooves 14 and other grooves 15 is formed on the designsurface 12, the upper limit of the aspect ratio Y may be 40 inconsideration of reliable prevention of appearance defects. Meanwhile,the lower limit of the groove depth, which is 0.3 [mm], is a valuedetermined by visibility. Accordingly, if Xd is 0.3 [mm], the upperlimit of the aspect ratio Y becomes 40. Instead of Expression 1, thefollowing Expression 2 is obtained by solving these simultaneousequations.

Y≧30, Xd≧0.3, Y≦−50Xd+55   (Expression 2)

Likewise, if the upper limit of the aspect ratio Y is adjusted,Expressions corresponding to Expressions 1 and 2 may be obtained bysolving the simultaneous equations while corresponding to the lowerlimit of the groove depth.

Each of Expressions 1 and 2 and the obtained Expressions is referred toas an aspect ratio function. The aspect ratio function is a linearexpression.

Operational Advantage of Condition 2

Condition 2 where the groove depth Xd is set to a length according tothe aspect ratio Y by Expression 1 or 2 is a condition (aspect ratiofunction) where one of the aspect ratio Y and the depth Xd of the groove14 is decreased when the other thereof is increased. Accordingly, eventhough the resin molding 11 includes a complex design surface 12 where aplurality of grooves 14 cross each other or a complex design surface 12that includes other grooves 15 such as letters or marks in addition tothe rectangular groove 14 formed on the design surface 12, it ispossible to secure high metallic feeling and to prevent the generationof appearance defects. Therefore, painting may not need to be performedon a garnish having the complex design surface 12.

<Metallic Tone Resin: Condition 3>

In Condition 3 of this embodiment, a mean particle diameter of thebright material 10 is in the range of 5 to 20 [μm].

That is, a mean particle diameter of the bright material 10 is optimizedin Condition 3. The reason why the lower limit is set to 5 [μm] is thatappearance defects are likely to be generated if a bright material 10having a particle diameter smaller than the mean particle diameter isused. That is, for example, if the same parts by weight of a brightmaterial 10 having a particle diameter of 1 [μm] as a bright materialhaving a particle diameter of 5 [μm] are added, the number of particlesis increased although the degree of a metallic tone is equal to thedegree of a metallic tone in the case of a particle diameter of 5 [μm].Therefore, appearance defects become more noticeable.

The reason why the upper limit of the mean particle diameter is set to20 [μm] is that an aspect ratio of about 30 can be obtained by this meanparticle diameter. That is, if a mean particle diameter is set to 27[μm], an aspect ratio may be lowered, so that metallic feelingdeteriorates. That is, even though only a mean particle diameter isincreased regardless of an aspect ratio, metallic feeling is notimproved.

Operational Advantage of Condition 3

In Condition 3, a mean particle diameter is set in the range of 5 to 20[μm]. Accordingly, it is possible to reduce cost by making a meanparticle diameter be relatively small, and to obtain metallic feelingcaused by an aspect ratio.

According to this embodiment as described above, when a part having agroove 14 on the design surface 12 thereof is molded by using a resinmaterial where a bright material 10 having an aspect ratio Y in therange of about 30 to 50 is added, it is possible to secure thevisibility of the part and to prevent the generation of the weld line 30and the flow mark 32 by performing molding while the groove depth andthe aspect ratio Y of the bright material 10 are in a diagonal rangeshown in FIG. 1.

A resin material, which contains a bright material 10 (of which anaspect ratio Y is in the range of 30 to 50) having high bright feelingand has been difficult to produce in large quantities due to problems ofappearance defects in the related art, can be used in this embodiment bydevising a resin material. Accordingly, even though the painting is notperformed, it is possible to obtain high metallic feeling like thepainting. For this reason, painting does not need to be performed, sothat it is possible to eliminate the generation and discharge ofvolatile organic compound (VOC) that are to be generated due topainting. Further, since a painting process does not need to beperformed, it is possible to reduce the number of processes and toreduce cost.

Embodiment 1

Embodiment 1 will be described below. In Embodiment 1, theabove-mentioned Conditions 1 to 3 will be described in detail andCondition 4 is applied. First, the amount of the added bright material10 (parts by weight) is examined. Then, a gate angle of Condition 4 willbe described. Condition 4 corresponds to characteristics of Embodiment 2(a manufacturing method) and Embodiment 3 (a metal mold).

<The Amount of Added Bright Material (Parts by Weight)>

A test piece 28 shown in FIG. 6 was produced, a prototype of a resinmolding that contained a bright material 10 having a relatively largeaspect ratio Y was made, and a relationship between the amount of theadded bright material 10 and strength of the test piece 28 was checked.Further, a hole 29 was formed at the test piece 28 so that the degree ofgeneration of a weld line 30 could be evaluated. Furthermore, the flowmark 32 was likely to be generated near the gate 26. The AES resin wasselected as a thermoplastic base resin, and a colorant was added.

The amount of the added bright material 10 needs to be determined inconsideration of impact resistance of a material, a color formingproperty, and material cost. As the amount of the added bright material10 is increased, metallic feeling is improved, so that it is possible tosecure a metallic tone having high quality feeling. However, impactresistance deteriorates and material cost is also increased. For thisreason, it is expected that metallic feeling is obtained by using asmaller amount of the added bright material.

In order to specify an effective amount of the added bright materialbased on 100 parts by weight of other materials and the AES resin, 0.5,1.0, 2.0, and 4.0 parts by weight of the bright material 10 (of which amean particle diameter is 5 μm and an aspect ratio Y is about 30) areadded, and Charpy impact strength, metallic feeling, and the degree ofgeneration of an appearance defect, such as a weld line 30 or a flowmark 32, were evaluated. Charpy impact strength was denoted by energycausing fracture, and was evaluated in accordance with ISO 179 (Type Anotch ISO 179/1 eA, 23° C.). The results thereof are shown in Table 1.

TABLE 1 The amount of the added bright material [parts by weight] 0 0.51.0 2.0 4.0 Charpy impact strength [kJ/m²] 13 11 10 10 11 Metallicfeeling — X Δ ◯ ◯ Weld line — X X X X Flow mark — X X X X

Charpy impact strength (23° C.) was reduced due to the addition of thebright material. However, significant difference did not appear in avalue of Charpy impact strength within the range of 0.5 to 4 parts byweight of the added bright material, and this range was a range wherethere was no problem in using the resin molding as a shift garnish. Ifthe amount of the added bright material is 1.0 part by weight, metallicfeeling could not be sufficiently secured. To secure sufficient metallicfeeling, 2.0 parts by weight or more of the added bright material neededto be added. Meanwhile, since the base material of an AES resin wasopaque, at least 2.0 parts by weight thereof needed to be added.However, even though 0.1 to 0.5 parts by weight of the bright material10 was added to a resin, such as a PMMA resin or a PC resin, of whichthe base material was transparent, metallic feeling could be secured. Inthe range of 0.5 to 4.0 parts by weight of the added bright material,difference did not appear in the degree of generation of the weld line30 and the flow mark 32. From the above-mentioned results, 2 parts byweight was decided as the amount of the added bright material.

Details of a molding material, where the amount of the added brightmaterial was set to 2 parts by weight and other factors were changed,are shown in Table 2. An AES resin was selected as a base resin, andfour kinds of bright materials of which mean particle diameters andaspect ratios Y were different from each other were added. As shown inTable 2, since metallic feeling is improved as an aspect ratio Y isincreased, but an appearance defect, such as a weld line 30 or a flowmark 32, is likely to be generated.

TABLE 2 Molding material 1 Molding material 2 Molding material 3 Moldingmaterial 4 Base resin AES resin AES resin AES resin AES resin MeanParticle 40 5 10 20 Diameter [μm] Aspect ratio about 10 about 30 about40 about 50 Added amount [parts  2 2  2  2 by weight] Metallic FeelingDo not exist Exist Significantly exist Significantly exist AppearanceDefect Be slightly likely to be Be likely to be Be very likely to be Bevery likely to be generated generated generated generated

<Condition 4: Gate Angle>

A relationship among the groove 14 of the resin molding, a gate position(angle), and the flowability of a resin at the time of injection moldingwill be described below.

FIG. 7 is a view showing an example where a gate is disposed in adirection of a long side of the groove of the design surface 12. Thegroove 14 includes short sides 16 and long sides 18. If a gate 26 isdisposed at an angle where a resin is supplied in a direction of thelong side 18, the flow of the resin becomes fast resin flow 20A on theoutside of the groove 14 and becomes slow resin flow 20B on the insideof the groove 14. As a result, the collision of a resin, which flows atan end of the long side 18 opposite to the gate 26, occurs, and thecollision position thereof is likely to be in a specific region.Further, since the collision occurs at a relatively high velocity, aweld line 30 is likely to be generated.

FIG. 8 is a view showing an example where a gate is disposed in adirection of a short side of the groove of the design surface 12. Inthis example, if a gate 26 is disposed at an angle where a resin issupplied in a direction of the short side 16, likewise, the flow of theresin becomes fast resin flow 20A on the outside of the groove 14 andbecomes slow resin flow 20B on the inside of the groove 14. However,since the collision position of the resin is not in a specific regionand the collision velocity thereof is also relatively low, a weld line30 is hardly generated as compared to the example shown in FIG. 7. Inparticular, considering that a time where the velocity of the resin flowin the groove 14 is reduced is short, velocity difference is small, andthe velocity of the fast resin flow 20A generated near the short side 16on the outside of the groove 14 becomes substantially equal to thevelocity of the slow resin flow 20B generated in the groove 14 untilcollision, the intensity of the collision of the resin is decreased. Inthe case of an angle shown in FIG. 8, an appearance defect such as theflow mark 32 of the region, which is denoted by reference region 24shown in FIG. 5, is likely to be generated depending on the groove depthXd.

Next, the optimization of the gate position (gate angle) is attempted inorder to adjust angles that are formed between the resin flows 20 andthe long and short sides 18 and 16 of the groove. A weld line 30 iscaused by the collision velocity of a resin and the size of a collisionregion. It is preferable that the resin flow be examined as a velocityvector from these and the velocity of the resin flow be uniformizedregardless of the presence of the groove 14. Further, a property wherethe resin flow becomes slow in the groove 14 may be added.

FIG. 9 shows a relationship (gate angle) between the groove 14 and thegate position. A resin was supplied from first to third gates 26A, 26B,26C that are represented by outline arrows of FIG. 9, and gate positionswere represented by 90, 70, and 45° that are angles with respect to thedirection of the long side 18 of the groove 14. The velocity vector ofthe resin flow at each of the gate angles is shown in FIG. 9. A firstgate 26A corresponds to the same disposition as the gate shown in FIG.8. A third gate 26C forms an angle of 45° with respect to the directionof the long side 18. A second gate 26B is slightly close to the angle ofthe third gate 26C in an angle range that is defined by the first andthird gates 26A and 26C. In this example, it is thought that thegeneration of a weld line 30 is suppressed as much as possible since avelocity vector is shortened at 45° of the third gate position 26C.

FIGS. 10A and 10B illustrate an example of an MT shift garnish. As shownin FIG. 10A, the MT shift garnish includes rectangular grooves 14 thatare formed in vertical and horizontal directions in the drawing andrepresent the operative position and direction of a shift lever, andother grooves 15 that represent letters. The other grooves 15 includenumerals 1 to 5 that denote gear positions, and a letter “R” thatdenotes a reverse position. FIG. 10B is a cross-sectional view takenalong a line A-A of FIG. 10A. A hook portion 13 of the resin molding 11is formed by undercutting, but is drawn at a slide core and fixes thegarnish by the hook portion 13.

As shown in FIG. 11, the shift garnish includes vertical grooves 14 athat each have a rectangular shape elongated in the vertical directionin the drawing, a horizontal groove 14 b that is formed in thehorizontal direction, and other grooves 15 that represent letters. Thevertical groove 14 a has curvature at the end thereof, but can beinterpreted as the groove 14 since the vertical groove 14 a has arectangular shape formed by the long side 18 and the short side 16. Theends of the horizontal groove 14 b are connected to the other grooves,but the horizontal groove is likewise the groove 14 that has arectangular shape.

In the example shown in FIG. 12, a metal mold was manufactured so thatinjection could be performed at three kinds of gate angles shown in FIG.9 while the vertical grooves 14 a formed at the center position of theshift garnish in a vertical direction in the drawing were used as axes.As shown in FIG. 12, the first gate 26A is provided on an extension lineof a horizontal straight line 14 b, and the second and third gates 26Band 26C are provided at positions that correspond to angles of 22.50 and450 from the first gate 26A with respect to the central portion of thepart, respectively.

When four kinds of materials shown in Table 2 were injected from each ofthe gates 26, the presence of a weld line 30 and a flow mark 32 wasevaluated. The groove depth Xd is set to three values, that is, 0.3 [mm]that is regarded to correspond to the lower limit of the visibility, and0.4 and 0.5 [mm] that correspond to more excellent visibility. Theresults thereof are shown in Tables 3 and 4. Table 3 shows the presenceof the weld line 30 and Table 4 shows the presence of the flow mark 32.

TABLE 3 Groove Molding Molding Molding Molding depth [mm] Gate material1 material 2 material 3 material 4 0.3 26A X X ◯b ◯b 26B X X X X 26C X XX X 0.4 26A X X ◯b; ◯l ◯b 26B X X X Δb; ◯l 26C X X X ◯l 0.5 26A X Δb; Δl◯b; ◯l ◯b; ◯l 26B X X Δb; Δl Δb; ◯l 26C X X ◯l ◯l LEGENDS: X: Notgenerated; Δb: Slightly generated from straight line b; Δl: Slightlygenerated from letter; ◯b: Generated from straight line b; ◯l: Generatedfrom letter.

TABLE 4 Groove Molding Molding Molding Molding depth [mm] Gate material1 material 2 material 3 material 4 0.3 26A X X X X 26B X X X X 26C X X XX 0.4 26A X X X ◯a 26B X X X ◯a 26C X X X Δa 0.5 26A X Δa ◯a ◯a 26B X XΔa ◯a 26C X X Δa Δa LEGENDS: X: Not generated; Δa: Slightly generatedfrom straight line a; ◯a: Generated from straight line a.

When molding was performed using a molding material [1] (of which a meanparticle diameter was 40 μm and an aspect ratio Y was about 10), a weldline 30 and a flow mark 32 were not generated from a groove-shapedportion regardless of a groove depth and a gate position. However,appearance had not metallic feeling, and had very emphasized plasticfeeling.

When molding was performed using a molding material [2] (of which a meanparticle diameter was 5 μm and an aspect ratio Y was about 30), a weldline 30 and a flow mark 32 were not generated in the cases of groovedepths of 0.3 and 0.4 [mm] even though the molding material was injectedfrom any gate 26. However, when the molding material was injected fromthe first gate 26A, a weld line 30 and a flow mark 32 were generated inthe case of a groove depth of 0.5 [mm]. In appearance, the same metallicfeeling as a painted-component was obtained.

When molding was performed using a molding material [3] (of which a meanparticle diameter was 10 μm and an aspect ratio Y was about 40), a weldline 30 was generated in the cases of groove depths of 0.3 and 0.4 [mm]only if the molding material was injected from the first gate 26A. Eventhough the molding material was injected from any gate 26, a weld line30 and a flow mark 32 were generated in the case of a groove depth of0.5 [mm]. In appearance, brightness is higher than the brightnesscorresponding to the molding material [2], high metallic feeling, aswell as a painted-component was obtained.

When molding was performed using a molding material [4] (of which a meanparticle diameter was 20 μm and an aspect ratio Y was about 50), a weldline 30 was generated in the case of a groove depth of 0.3 [mm] only ifthe molding material was injected from the first gate 26A. Even thoughthe molding material was injected from any gate 26, a weld line 30 and aflow mark 32 were generated in the cases of groove depths of 0.4 and 0.5[mm]. In appearance, brightness is higher than the brightnesscorresponding to the molding material [2], high metallic feeling, aswell as the painted component was obtained.

Meanwhile, the followings were found out from these evaluation results.When a resin flowed in a direction parallel to the direction of the longside of the groove, a weld line 30 was likely to be generated. Further,as the length was large in the direction of the long side, a weld linetended to be easily generated. When a resin flowed in a directionorthogonal to the direction of the long side of the groove-shapedportion, a flow mark 32 was likely to be generated. Furthermore, as thelength was large in the direction of the long side, a flow mark tendedto be easily generated. It is preferable that a gate be provided at aposition so that a resin does not flow in a direction parallel ororthogonal to the direction of the long side of the groove-shapedportion during the molding as much as possible.

Difference Between First and Second Gates 26A and 26B

When the groove depth Xd is 0.5 [mm] in the case of the molding material[2] of Tables 3 and 4, the results of the generation of the defects ofthe first gate 26A and the second gate 26B are different from eachother. Further, when the groove depth Xd is 0.4 and 0.5 [mm] in the caseof the molding material [3], the results of the generation of the weldline 30 are different from each other.

For this reason, if the gate angle is in the angle range of 45°±30° whenthe direction of the long side of the groove is regarded to correspondto 0°, it is possible to prevent the generation of defects and theaspect ratio Y. This angle range is shown by θ1 of FIG. 9. Meanwhile,the angle of the gate 26C corresponds to “the direction of 45° when thedirection of the long side of the groove is regarded to correspond to0°”, and an angle obtained by adding 90° to 45° is the same angle. θ1 isthe range of an angle, which is larger than an angle corresponding tothis direction by 30°, to an angle, which is smaller than an anglecorresponding to this direction by 30°.

Difference Between Second and Third Gates 26B and 26C

When the groove depth Xd is 0.5 [mm] in the case of the molding material[3] in Table 3, the results of the generation of a weld line 30 of thegroove 14 b are different from each other. Further, when the groovedepth Xd is 0.4 and 0.5 [mm] in the case of the molding material [4],the results of the generation of a weld line 30 of the groove 14 b aredifferent from each other.

When the groove depth Xd is 0.4 and 0.5 [mm] in the case of the moldingmaterial [4] in Table 4, the results of the generation of a flow mark 32are different from each other.

For this reason, if the gate angle is in the angle range of 45°±10° whenthe direction of the long side of the groove is regarded to correspondto 0°, it is possible to prevent the generation of defects and theaspect ratio Y. This angle range is shown by θ2 of FIG. 9.

Operational Advantage of Condition 4

From the above description, if the angle θ1 or θ2 of a resin flow ofCondition 4 is applied, it is possible to obtain very high metallicfeeling by using a bright material having a large aspect ratio Y, and toeffectively prevent the generation of appearance defects, such as a weldline 30 and a flow mark 32. Further, if an aspect ratio Y of the brightmaterial and a groove depth Xd with respect to the thickness Xt of theresin molding are made in the ranges of Condition 2, it is possible tosecure the visibility of a part, to prevent the generation of a weldline 30 and a flow mark 32, and to obtain a part that has the same highdesign properties as a painted-component.

Condition 4 and the combination of Conditions 4 and 2 may be appliedwhen the appearance of a part needs to be improved without painting aresin part. In particular, Condition 4 and the combination of Conditions4 and 2 may be applied not to perform painting a resin part made of amolding material to which a bright material, such as aluminum powder ormica powder, is added.

Embodiment 2

Embodiment 2 of this embodiment will be described below.

<Manufacturing Method: Condition 4>

FIG. 13 is a partial view cross-sectional view showing an example of aplate 50 that is used in Embodiments 2 and 3. The plate 50 issuperimposed on another plate (not shown), so that a cavity 52 havingthe shape corresponding to the design surface 12 shown in FIG. 10A isformed. A resin is supplied into the cavity 52 so as to fill the cavityand is hardened by cooling or the like, so that a product (a resinmolding, for example, an MT shift garnish) is formed.

Further, a gate, which connects a plate 50 to a runner 54 of aninjection molding machine, is disposed at an angle (45°) shown in FIG.13 in order to make a resin supply angle (gate angle), which is formedwith respect to the direction of the long side 18 of the groove 14, bein the ranges of θ1 and θ2 of Condition 4.

Referring to FIG. 14, in a manufacturing method of Embodiment 2, first,a cavity 52 corresponding to the shape of a molding 11 that hasrectangular grooves 14 on a design surface 12, and a gate 26 through aresin flows into the cavity are formed by superimposing a plurality ofplates 50 (Step S1).

After that, a resin, which contains 0.1 to 4 parts by weight of a brightmaterial such as aluminum powder based on 100 parts by weight of athermoplastic resin, is injected to the cavity 52 through the gate 26(Step S2). In this case, in Embodiment 2, a gate angle is made in therange of 45°±30° (θ1 shown in FIG. 9) when the direction of the longside of the groove is regarded to correspond to 0°, and a resin flowsfrom the gate 26 corresponding to this angle. Further, when the aspectratio Y or complexity of the design surface 12 is increased, the gateangle may be in the range of ±10° (02 shown in FIG. 9).

Subsequently, the resin is hardened by cooling or the like (Step S3),and the resin moldings are extracted by separating the plates 50 (StepS4).

If a resin containing the bright material 10 is supplied in the range ofthe gate angle θ1 or θ2, it is possible to make the degree of theappearance defects deteriorate even though appearance defects, such as aweld line 30 or a flow mark 32, are generated in the case of anotherangle (for example, an angle of the gate 26A shown in FIG. 9), or toprevent the generation of the appearance defects.

<Manufacturing Method: Conditions 4, 2, and 3>

As a method of manufacturing resin molding, a molding material, a groovedepth Xd, and a gate angle may be optimized in order to obtain very highdesign properties. In this case, an aspect ratio Y and a groove depth Xdare in a predetermined range in accordance with the above-mentionedCondition 2.

That is, if the aspect ratio of the bright material is denoted by Y andthe groove depth is denoted by Xd [mm], the aspect ratio Y and thegroove depth Xd are in the range of Expression 1 or 2. That is, theaspect ratio and the groove depth are in the range of Condition 2. Thedepth of the groove is formed by the plates of the metal mold.

In this case, in Step S1 illustrated in FIG. 14, if the plates aresuperimposed, a cavity 52 having the groove depth Xd in the range ofCondition 2 or 3 is formed. Further, in Step S2, a resin containing abright material, which has an aspect ratio Y in the range of Condition 2or 3, flows into the cavity.

Furthermore, a mean particle diameter of the bright material 10 may bein the range of Condition 3.

If the ranges of Conditions 2, 3, and 4 are satisfied, it is possible toprevent the generation of appearance defects as shown in Tables 3 and 4even though the shape of the design surface 12 is complex as shown inFIG. 10A.

Embodiment 3

Embodiment 3 of this embodiment will be described below.

<Metal Mold: Condition 4>

FIG. 15 is a view showing an example of a metal mold, which forms tworesin moldings, according to the invention, and is a plan view showingthat resin moldings are placed on one plate 50. As shown in FIG. 15, ametal mold for a metallic tone resin molding of Embodiment 3 includescavities 52 corresponding to the shape of a molding 11 that hasrectangular grooves 14 on a design surface 12, gates 26 through a resincontaining a bright material 10 flows into the cavities 52, a sprue 56that injects a resin to the gates through runners 54, and a plurality ofplates 50 that forms the cavities 52.

Further, in Embodiment 3, according to Condition 4, the gate 26 isprovided in the range of 45°±30° (θ1 shown in FIG. 9) when the directionof the long side of the groove 14 is regarded to correspond to 0°.Furthermore, when the aspect ratio Y or complexity of the design surface12 is increased, the gate angle may be in the range of ±10° (θ2 shown inFIG. 9).

FIG. 16 is a cross-sectional view taken along a line A-A of FIG. 15. Twoplates 50 are superimposed, and the plates are superimposed so thatpartings 58 are aligned, thereby forming the cavity 52. In themanufacturing method illustrated in FIG. 14, a resin containing a brightmaterial 10 is injected to the cavity 52 and hardened, thereby forming aresin molding 11. Subsequently, the plate 50 is separated in a verticaldirection of FIG. 16, and resin moldings are extracted.

FIG. 17 shows an economic metal mold of Embodiment 3, which forms fourresin moldings and is obtained by the combination of the metal moldsshown in FIG. 15. In this example, the area and volume of the metal moldis reduced as much as possible, and it is possible to form four moldingsby one time molding. Accordingly, it is possible to further improveproductivity.

Further, in the example shown in FIG. 17, a metal mold includes fourcavities 52 that are disposed around the sprue 56 at the same distancefrom the sprue 56 at an interval of 45°. The metal mold includes runners54 that supplies a resin to the cavities 52 from the sprue 56therethrough, have the same shape and length, and are disposed at aninterval of 45°. The runners 54 are connected to gates 26 of thecavities 52. Furthermore, the directions of the gates 26 are determinedso that the direction of the resin molding in the cavity 52 is in therange of a gate angle θ1 or θ2 of Condition 4.

In the example shown in FIG. 17, assuming that a numeral “3” of a resinmolding corresponds to the upper side and a numeral “4” corresponds tothe lower side, the design surface 12 is oriented in the cavity 52 so asto form an angle of 135° (45°±90°) with respect to a vertical direction.Accordingly, a metal mold for four moldings is formed, the cavities 52have the same gate angle, and it is possible to reduce the area of themetal mold as much as possible.

In addition, since the runners 54 of the four cavities 52 are formed atan interval of 45° and have the same shape and length, it is possible tomake the supply state or thermal change of a resin be the same as eachother.

Meanwhile, the size of a metal mold and a molding machine should beincreased in order to form eight or sixteen moldings. Further, if thesize of the metal mold and the molding machine is increased, the lengthof the runner 54 is increased. For this reason, a resin is partiallycooled in the runner 54. If the cooled resin is pushed by a resin to besupplied from the rear side and enters a product, a lump of the cooledresin appears on the design surface 12 and causes an appearance defect.Further, if flow length is increased, some kinds of resins cause shortshot (are not filled), so that a yield is decreased.

According to the constitution shown in FIG. 17, the length of the runner54 is short and these problems are not generated even in a metal moldfor a plurality of moldings.

<Metal Mold: Conditions 4, 2, and 3>

A molding material and a groove depth Xd may be optimized in order toobtain very high design properties like in the Embodiment 2 by using ametal mold for a resin molding. In this case, an aspect ratio Y and agroove depth Xd are made in a predetermined range in accordance with theabove-mentioned Condition 2 or 3.

That is, if the aspect ratio of the bright material 10 is denoted by Yand the groove depth is denoted by Xd [mm], the aspect ratio Y and thegroove depth Xd are in the range of Expression 1 or 2. That is, theaspect ratio and the groove depth are in the range of Condition 2. Theaspect ratio Y is achieved by a molding material.

In this case, the groove depth Xd shown in FIG. 10B is adjusted by theplates 50 of the metal mold of Embodiment 3, depending on the aspectratio Y.

A mean particle diameter of the bright material 10 may be in the rangeof Condition 3.

Even though the shape of the design surface 12 is complex as shown inFIG. 10A, it is possible to prevent the generation of the appearancedefects as shown in Tables 3 and 4 in the range of Conditions 2, 3, and4.

While the present invention has been shown and described with referenceto certain exemplary embodiments thereof, it will be understood by thoseskilled in the art that various changes in form and details may be madetherein without departing from the spirit and scope of the invention asdefined by the appended claims.

1. A resin molding, comprising: a main body which is comprised of 100parts by weight of thermoplastic resin and 0.1 to 4 parts by weight ofbright material having the aspect ratio of 30 to 50, wherein a main bodyhas a design surface formed with a groove; and wherein the lower limitof the depth of the groove is set to 0.3 mm and the upper limit of thedepth of the groove is set to 0.5 mm.
 2. The resin molding as set forthin claim 1, wherein Y and Xd [mm] satisfy the following expressions:Y≧30;Xd≧0.3; andY≦−100Xd+80, where Y denotes the aspect ratio of the bright material andXd denotes the depth of the groove.
 3. The resin molding as set forth inclaim 1, wherein Y and Xd further satisfy the following expression:Y≦−50Xd+55.
 4. The resin molding as set forth in claim 1, wherein thebright material has the mean particle diameter of 5 to 20 μm.
 5. Theresin molding as set forth in claim 1, wherein the groove is formed intoa rectangular shape on the design surface.
 6. A method for manufacturinga resin molding, comprising: laminating a plurality of plates to form acavity and a gate through which resin material is injected into thecavity; injecting the resin material which is comprised of 100 parts byweight of thermoplastic resin and 0.1 to 4 parts by weight of brightmaterial, into the cavity through the gate; hardening the resin materialto form the resin molding; and separating the plates to extract theresin molding from the cavity, wherein the plates are formed such thatthe resin molding includes a main body having a round-shaped designsurface formed with a plurality of rectangular-shaped grooves, thelongest groove of which extends in a first direction; and wherein theplates are formed such that the gate extends toward a center of theround-shaped design surface and at an angle range of 45°±30° withrespect to the first direction.
 7. The method as set forth in claim 6,wherein the plates are formed such that the gate extends at an anglerange of 45°±10° with respect to the first direction.
 8. The method asset forth in claim 7, wherein the plates are formed such that the gateextends at an angle of 45° with respect to the first direction.
 9. Themethod as set forth in claim 6, wherein the bright material has theaspect ratio of 30 to 50, wherein the plates are formed such that thelower limit of the depth of the grooves is set to 0.3 mm and the upperlimit of the depth of the grooves is set to 0.5 mm.
 10. The method asset forth in claim 9, wherein the plates are formed such that Y and Xd[mm] satisfy the following expressions:Y≧30;Xd≧0.3; andY≦−100Xd+80, where Y denotes the aspect ratio of the bright material andXd denotes the depth of the groove.
 11. The method as set forth in claim10, wherein the plates are formed such that Y and Xd further satisfy thefollowing expression:Y≦−50Xd+55.
 12. The method as set forth in claim 6, wherein the brightmaterial has the mean particle diameter of 5 to 20 μm.
 13. A metal moldfor manufacturing a resin molding, comprising: a first plate formed witha sprue; and a second plate; wherein the first plate and the secondplate are formed such that a cavity, a gate and a runner are formed whenthe first plate is laminated on the second plate so that resin materialis injected from the sprue into the cavity through the runner and thegate to form the resin molding; wherein the first plate and the secondplate are formed such that the resin molding includes a main body havinga round-shaped design surface formed with a plurality ofrectangular-shaped grooves, the longest groove of which extends in afirst direction; and wherein the first plate and the second plate areformed such that the gate extends toward a center of the round-shapeddesign surface and at an angle range of 45°±30° with respect to thefirst direction.
 14. The metal mold as set forth in claim 13, whereinthe first plate and the second plate are formed such that the gateextends at an angle range of 45°±10° with respect to the firstdirection.
 15. The metal mold as set forth in claim 14, wherein thefirst plate and the second plate are formed such that the gate extendsat an angle of 45° with respect to the first direction.
 16. The metalmold as set forth in claim 13, wherein the first plate and the secondplate are formed such that the lower limit of the depth of the groovesis set to 0.3 mm and the upper limit of the depth of the grooves is setto 0.5 mm.